Fungicides add value despite low disease pressure

In a typical growing season, nearly every soybean field can be susceptible to some type of crop disease. From soybean white mold in the northern states to aerial web blight in the mid-South, fungal disease can put a damper on soybean yields.

Soybean prices have dropped from historical highs, but remain at profitable levels. To get the most from their genetics investment, growers are paying more attention to the value of early- and mid-season fungicide applications.

Kent VanderWal, who farms in Brookings County in east-central South Dakota, knows soybean white mold can take a significant bite out of soybean yield. The disease thrives in cool wet weather, especially during the spring when cool, humid weather and moist soils persist. VanderWal had those conditions in mind when he decided to conduct soybean fungicide yield trials in 2012.

But 2012 was not a typical growing season and most of the nation faced drought conditions. Below-normal precipitation resulted in very low disease pressure in Vanderwal¹s plots, even the untreated check plots.

"Because disease pressure was so low, we did not notice any visible difference when comparing the foliage of treated and untreated plots in our fungicide trials," says VanderWal. "They all looked good, with few, if any, signs of disease."

Low disease pressure during a hot, dry season did not surprise VanderWal. What did surprise him was the extra yield the fungicide-treated plots delivered at harvest.

"One fungicide treatment produced five to six more bushels per acre than untreated plots," VanderWal reports.

One product used in the trial, DuPont Aproach fungicide, was in development in 2012 and is available to soybean, corn and wheat growers for the 2013 season. Bond McInnes, fungicide development manager with DuPont Crop Protection, says VanderWal's results are consistent with what he¹s seen in yield comparisons from other fungicide field research.

"Large-plot soybean trials with Aproach in 2011 and 2012 showed improved yield in 25 of 35 trials by an average of 3.6 bushels per acre over untreated plots, when treated with a preventive early-season and mid-season fungicide application," says McInnes. "Both years, we experienced unusually hot, dry growing seasons."

Whether the yield is coming from control of low levels of diseases or there are physiological benefits from the fungicide applications is yet to be determined, says McInnes.